Electronic locking systems have been widely used for controlling access to secured enclosures such as security and fire safes. Such locking systems typically have an electronic control module with an input device, such as a keypad, for entering an access code, and an access-control solenoid for controlling the operation of a locking mechanism. When the access code is determined to be valid, the solenoid is energized to retract its plunger, thereby permitting the locking mechanism to be unlocked. Due to considerations such as integrity of the enclosure, cost of construction, ease of installment, space constraints, etc., the electronic control module of the electronic locking system is typically mounted on the exterior of the secured enclosure, with wires leading to the access-control solenoid mounted inside the secured enclosure. U.S. Pat. No. 5,617,082, entitled "Electronic Access Control Device Utilizing a Single Microcomputer Integrated Circuit," describes a useful, cost effective and easily manufactured electronic locking system designed for such placement.
A general problem associated with placing the electronics of a locking system on the exterior of a secured enclosure is the vulnerability to tampering. In the case of a locking mechanism controlled by a solenoid, the electronic locking system may be defeated by "hot-wiring," in which case a tamperer severs the wires leading to the solenoid and applies a DC voltage to the wires, thereby energizing the solenoid to retract its plunger.